1. Field of the Invention
The invention relates to an actuator for switching a switching unit and including a mechanical display having a window and a display face discernible through the window.
2. Description of the Related Art
Electromechanical control units are used extensively to operate and control machines and installations. Such units come in various forms, for example, as pushbuttons, toggle switches, key switches or emergency off switches. Control units are mounted on control panels, operator panels, switch cabinet doors or housing covers. By manual actuation of the control units, electrical changes to the switching state and thus the desired control effects are brought about. Control units are equipped as standard with a mechanical display in order to display prevailing switching states, where the mechanical display may alternatively or additionally be equipped with an illuminable or illuminated unit.
Control units generally have a modular structure. This means that they consist of a pressure knob, a fastening part, such as a ring nut or a mounting holder, and at least one switching element or a plurality of switching elements which are formed as make-contact or break-contact elements. For assembly, the actuator is generally guided from the front through a hole in the control panel and mounted from the rear via a fastening part. The switching elements are mechanically fastened to the actuator or to the fastening part by screws, snap-fits or catches. The electrical connection of the switching elements to the control occurs via connection terminals.
In safety applications, such as emergency off control units, it is stipulated that the signal be generated by the opening of positive-opening contacts. Consequently, in the case of an unactuated emergency off control unit, the contacts and thus the associated circuit are closed. In the event of a fault or emergency, the break contact is interrupted by the emergency off actuator, which is located in front of the control panel, being struck and the installation or machine is thus transferred into a safe state. However, this only works if the spatial assignment between the actuator and switching element is ensured. As a result of defective mounting or of violent impacts, it is possible for the switching elements to become mechanically separated from the actuator. In this case, the emergency off control unit is no longer operational. As a result, in the event of actuation in an emergency, the contacts are not opened and thus the hazardous state is also not rectified. This can have fatal consequences for humans and machinery. Therefore, the secure connection between the actuator and switching elements is of considerable importance.
The demand for an integrated optical display, which may be both a mechanical and/or an electrical switch display, causes problems with regard to the accommodation of the necessary components, because the overall volume of the unit can be varied only within narrow boundaries, in particular as a result of a standardized construction diameter of 22.5 mm, for example. Hitherto, when it was not possible to integrate the display in the control unit, an additional control station, such as having a signal lamp, was added. On account of the additional space requirement, for example, on a control panel of the installation unit and the necessary use of a separate display, this solution is disadvantageous.
To this end, DE 102007046999 B3 discloses an actuator that is provided for switching a switching unit and that has a mechanical display, where the mechanical display includes a window and a display face that is discernible through the window. Here, the display face is connected to a spring web attached to an actuating part of the actuator and is provided for partial rotation about a rotation axis together with at least one part of the spring web during an actuating movement of the actuating part. Here, the rotation axis is oriented substantially perpendicularly to the actuating movement of the actuating part.
The disadvantage of this conventional actuator the prior art is that the mechanical display face is guided via very slender mechanical components which, on account of the confined space in the control unit, can easily tilt or deform and consequently no longer allow the control unit to be operated as stipulated.